1. Field of the Invention
Exemplary aspects of the present invention relate to the use of a thermoelectric device to recover waste heat from a semiconductor device in a power electronic system of a hybrid electric vehicle.
2. Discussion of the Background
It is widely known that land vehicles, including automobiles, have a large influence on the global environment. One such environmental impact concerns the production and transport of fuel required for vehicles. A second environmental impact is the resultant emissions that are a byproduct of the combustion of the fuel utilized by vehicles for propulsion.
Next generation vehicles, including hybrid electric vehicles, are one of several ways of addressing the need to reduce the expenditure of non-renewable fuels. Hybrid Electric Vehicles increase the overall (sometimes called well-to-wheel) efficiency of the vehicle by supplementing the power requirements of the combustion engine with an electric machine. Accordingly, hybrid electric vehicles exhibit twin environmental benefits of using less fuel and emitting fewer pollutants. Though typically more fuel efficient than conventional combustion vehicles, hybrid electric vehicles are also optimized to achieve higher levels of efficiency.
The propulsion drive of a Hybrid Electric Vehicles typically consists of a combustion engine and one or more electric drive components. These electric drives or electric machines are arranged in either series or parallel with the combustion engine.
In a series arrangement, the electric machine(s) typically provide all of the motive force for the vehicle and the combustion engine typically provides a means for providing electric energy for the electric machine(s). A single electric machine may be used in conjunction with a power splitting device, such as a differential, to provide the motive force to the vehicle wheels. Alternatively, multiple electric machines may be coupled through gear reductions and shafts to the wheels, or so-called wheel-motors may be integrated into the wheel hubs.
A fuel cell engine may be substituted for the combustion engine in a series hybrid electric vehicle arrangement. Other means of producing electric energy such as gas turbines, hydraulic motors, or the like may also be substituted.
Conversely, in a parallel Hybrid Electric Vehicle arrangement the combustion engine and the electric machine(s) each provide motive force for the vehicle. That is, torque from the engine is combined with torque from the electric machine(s) to propel the vehicle. A single electric machine is typically provided along the output shaft of the engine prior to the input shaft of the transmission. Alternatively, wheel motors may provide torque to axle shafts that are propelled by the combustion engine.
Hybrid Electric Vehicles may also combine series and parallel architectures. Such a system combines the electric machines and the combustion engine such that an electric machine may provide motive force alone or in parallel with the combustion engine. Furthermore, in the series/parallel Hybrid Electric Vehicle system another electric machine may simultaneously generate electricity or also provide motive force. This architecture sometimes called a power-split hybrid electric drive, can seamlessly change between engine-only, electric-only, or engine and electric propulsion.
Regardless of the particular architecture, the electric machines of a Hybrid Electric Vehicle are typically operated by alternating current (AC). The electric machines may be of the synchronous or asynchronous variety. One example of a synchronous AC machine is a permanent magnet machine which utilizes permanent magnets in the rotor to induce an electric field. A typical asynchronous electric machine in a hybrid electric machine may be an AC induction machine that utilizes an AC current to induce the magnetic field in the rotor.
Hybrid Electric Vehicles often utilizes an electrical energy storage device such as a battery, ultra-capacitor or the like. These energy storage devices store energy for usage by the electric machines. The ability to store electric energy and later use this energy to provide motive force, is one reason a Hybrid Electric Vehicle is more energy efficient than a conventional vehicle. The energy storage device typically transfers the stored electric energy to electric machines via direct current.
The electric machines of a Hybrid Electric Vehicle are typically operated via 3-phase alternating current which energize poles of the stator causing the rotor to rotate. This 3-phase alternating current is typically provided by a power inverter which inverts the DC energy from the energy storage device into 3-phase AC for use by the electric machines.
Power inverters may include several power modules which include several power devices. These power devices are switches which change the single phase direct current into 3-phase alternating current. The power devices may be one of an Insulated Gate Bipolar Transistor (IGBT), Metal Oxide Semiconductor Field-Effect Transistor (MOSFET), Schottky diode, etc.
Power devices produce heat while operating that must be dissipated to maintain performance. Typically the excess heat is managed in order to maintain operation of the power device. Excess heat can cause premature failure of the power device or may cause the power device to operate inefficiently.
Power electronic systems are typically cooled by heat sinks, water jackets, so-called cold plates and the like. Typically the power electronic systems dissipate heat via one of these devices to a fluid which carries the heat away from the power electronic device. These fluids may be gaseous (air for example) or liquid (water for example).
As with many technologies, the trend in power electronics systems is to create higher power density devices with a smaller size. However, the increase in power density of the power electronic system also necessitates improvements in heat dissipation.
Furthermore, increasing the thermodynamic efficiency is a common goal of many devices. One known means of increasing the thermodynamic efficiency of a system is through the use of thermoelectric devices.
One application of a thermoelectric device is to provide electric power based on a temperature differential. When opposite junctions of a thermoelectric device are respectively heated and cooled, a voltage potential is created by the temperature differential. This “Seebeck” voltage can then be used as a power source.
Land vehicles have utilized thermoelectric devices to make use of the Seebeck effect for the direct conversion of waste heat of a combustion engine into electricity. In particular, thermoelectric devices have been arranged in between an exhaust pipe and a heat sink in order to produce electricity.